This invention relates to a latch needle for knitwearmaking machines and is of the type which has a shank carrying a needle hook at one end. The shank is provided with a sawslot extending parallel to the shank length, and a needle latch is pivotally supported by a rivet disposed in the sawslot. In the region underneath the rivet, the sawslot has an aperture open at the back of the needle shank. The sawslot is bilaterally bounded by elastically deformable shank cheeks which, in the region of the upper edges of the sawslot, have supporting surfaces which cooperate with engagement faces provided on the latch back. Further, the sawslot is subdivided into portions of different widths.
To dampen the impact of the needle latch on the needle shank at the end of the reverse latch movement away from the needle hook to thus avoid damages to the needle and the latch particularly when the knitting machine operates at high speeds, it is known--as disclosed, for example, in German Patent No. 2,714,607--to design the latch-receiving sawslot in the shank such that a first, short sawslot portion (which contains the throughgoing aperture below the rivet) is adjoined by a second sawslot portion which projects beyond the end of the opened latch (when it is in its open, reverse position) and which is deeper than one-half the height of the needle shank. The supporting surfaces provided on the needle shank which cooperate with the engagement faces on the needle latch are situated above the second sawslot portion. By virtue of the cooperation of the needle shank cheeks flanking the sawslot, with the wedge-like converging flanks at the latch back, the shank cheeks, upon impact of the needle latch, are elastically spread apart while, at the same time, friction is generated at the supporting surfaces. In this manner a significant damping of the impact is achieved which ensures a gentle operation of both the latch and the needle shank. The wedge shape of the supporting surface on the latch back is obtained by rounding the latch back in the usual manner. Further, by virtue of this design the latch remains in the fully opened position and preserves its free mobility in this position, that is, the latch is not jammed between the cheeks of the needle shank.
A latch needle of the above-outlined type has been found to function in a highly satisfactory manner. It requires, however, a very accurate positioning and a particularly shaped design of the embossment which is pressed on the upper side of the needle shank and which constitutes the supporting surfaces for the needle latch. Further, as the needle shank thickens, the elastic deformability of the shank cheeks diminishes.
An essentially similar latch needle is disclosed in German Offenlegungsschrift (application published without examination) 33 35 908, according to which the sawslot is divided into first and second parts. The first part which is provided with a throughgoing aperture underneath the latch rivet, is dimensioned in its width in the usual manner and thus corresponds to the dimensions of the needle latch. The second sawslot part adjoins the first sawslot part on that side which is oriented away from the needle hook. The second sawslot part has a lesser width than the first sawslot part. The width of the narrower, second sawslot part is approximately 0.5 to 0.8 times the width of the first, wider sawslot part. The supporting surfaces for the latch back are arranged at the upper edges of the second, narrower sawslot part which too, has a throughgoing aperture opening at the needle back. The narrowing of the sawslot leads to correspondingly thicker shank cheeks and thus, to a reduced elastic deformability thereof.
To improve the elasticity of the shank cheeks in the region of the supporting surfaces for the latch back and to thus increase the desired dampening of the motion of the latch upon its impact on the engagement faces, in a latch needle known from German Offenlegungsschrift 43 24 232 a throughgoing aperture has been provided which fully separates the two shank cheeks and which extends from the supporting surfaces to the shank back. The width of the throughgoing aperture may be larger or smaller than or equal to the width of the sawslot in the region of the latch rivet. If such an aperture extends in the length dimension of the shank up to a location below the latch rivet--which is expedient to ensure a trouble-free lint removal--the danger exists that the latch support (latch bearing) becomes unstable. If, on the other hand, as it has been suggested in the alternative, at the needle back a bridge is provided underneath the latch rivet, then the lint removal is interfered with. The further suggested arrangement of two apertures extending in the longitudinal direction and being separated by a bridge at the needle back is not feasible partly because of the insufficient stability and partly because of manufacturing reasons.